For the transmission of high frequency energy through the atmosphere or in hollow bodies, antenna arrangements are known, which radiate electromagnetic high frequency waves in these media, whereby the high frequency waves also can again be received via such antenna arrangements. Such antenna arrangements serve for the conversion of electrical signals into electromagnetic waves or electromagnetic waves into electrical signals. These arrangements are used for information transmission or for evaluating the transmission space. Especially in the measurement technology, often spacing distances, speeds or the distribution of solid bodies or particles in dielectric media are detected through use of high frequency waves in the microwave frequency range, and the magnitude or quantity thereof are evaluated through special evaluating or measuring apparatuses. For that purpose, the solid bodies or particles to be measured must come into the radiation emission area, or the radiation emission area must be directed onto the measurement objects, whereby the radiation emission can be achieved by variously embodied antenna arrangements.
A method and an apparatus for the measurement of the volume proportion of a multi-phase flow in a pipeline by means of microwave radiation is known from the EP 0 703 447 B1. For that purpose, a row of microwave antennas are arranged on the circumference of the pipeline being flowed through, whereby the microwave antennas feed microwave energy into the pipeline, whereby the coupled-in microwave energy is simultaneously detected by a different microwave antenna. By integrating the coupled-out microwave energy, the particle volume proportion present in the flow is determined in the spread-out or propagated microwave field. For that purpose, twelve dipole antenna pairs are arranged symmetrically on the circumference of the pipe, whereby the dipole antenna pairs radiate the microwave energy orthogonally to the flow direction and perpendicularly to the radial direction into the pipeline being flowed-through. The dipole antenna pairs involve cross-wise arranged dipoles, which consist of a plurality of small pipe pieces welded together with one another, and which are arranged on the circumference of the pipe inner wall. Such antennas are very complicated or costly in the production and can impair a through-flowing multi-phase particle flow at least with smaller pipe cross-sections, so that such antennas are preferably utilized for larger pipeline diameters.
A further microwave measuring method for mass flow determination of a particle flow or stream in a round pipe-shaped hollow body is known from the DE 101 37 009 C1. For that purpose, an opening is provided in the pipe wall, into which opening a horn antenna is set-in or inserted, by which horn antenna microwave energy produced by a Gunn diode is coupled into the pipe interior via a hollow conductor or waveguide. These electromagnetic waves radiated into the flow channel are reflected by the particle stream and are simultaneously again received by the horn antenna and are supplied to a Schottky diode as a reflection receiver. Thereby, the measure or degree of reflection represents a function of the electromagnetic radiation reflected by the solid material proportion or component over the cross-section of the flow channel. The differential quotient according to time is formed from the time progression or course of the measurement signal, whereby this differential quotient represents a measure for the concentration of the particle distribution in the measurement area. Through a subsequent bridge rectifier circuit, the integral is mathematically formed from the derived measurement signal, whereby the magnitude value of the integral is to represent a measure for the mass through-flow in the flow channel. In that regard, the horn antenna radiates the microwave energy into the flow channel essentially only over the cross-section, so that only a small measurement range or area can be utilized in the axial direction, and only a limited measurement accuracy should be achievable therewith.
A further microwave measuring arrangement is known from the DE 44 06 046 C2, with which measuring arrangement a powder mass flow in a pneumatic conveying line is quantitatively determinable. For that purpose, a microwave resonator is arranged or mounted on the outer casing of the conveyor line, whereby this microwave resonator essentially consists of a resonance space or chamber, in which a high frequency antenna produces a microwave field. Since the conveyor line is apparently embodied as a plastic hose, the electromagnetic microwaves penetrate through the conveyor line wall and are damped in their amplitude and changed in their resonance frequency by the through-flowing mass particles. Thereby, the powder mass per unit volume is measured in the pipe interior. Simultaneously, still additionally, the speed of the through-flowing particle stream is detected by means of two spaced apart electrodes, and the conveying magnitude or the through-flow quantity is calculated by means of the measured volume mass. Such a coupling-in of microwaves, however, has a poor efficiency or degree of effectiveness, because the majority of the produced microwave radiation is radiated away outside of the pipe and therefore can no longer be coupled-out for the measurement signal evaluation. Such a measuring arrangement therefore requires a relatively high microwave energy for radiating-in, or a high measurement technology evaluation effort or expense, in order to achieve a sufficient measuring accuracy.
A further microwave measuring method and a corresponding apparatus is known from the EP 0 717 269 A2, in which the mass throughput is detectable in a pipe-shaped pneumatic conveyor line. For that purpose, for feeding-in microwaves, three coupling openings are provided on the circumference of the pipe wall, and the microwave energy is delivered to the coupling openings by means of hollow conductors or waveguides, coaxial conductors or strip line conductors, and can be coupled into the pipe-shaped conveyor line. At an axial spacing distance from the in-coupling openings, further similar out-coupling openings are mounted or arranged in the pipe wall, through which the coupled-in microwave energy is again coupled out. In order that also a multi-phased fluctuating particle flow is sufficiently accurately detectable over the entire conveyor line cross-section, three in-coupling and three out-coupling openings are provided, into which the microwave energy is coupled-in and coupled-out in a pulsed fashion one after another. For the determination of the conveying magnitude, the out-coupled microwaves are compared with a reference value without conveyor line loading, both after the damping thereof in the amplitude, as well as after the phase shifting thereof. In that regard, the deviation from this reference value is proportional to the loading density on the measurement section or path. Through a cross-correlation, the conveying speed is additionally determined, from which the conveying magnitude or the mass flow can be calculated by multiplication with the loading density on the measurement section.
The coupling openings or slots utilized in that regard feed the microwave energy basically uniformly into both axial pipe directions, so that maximally 50% of the supplied microwave energy is available for evaluation in the measurement direction. For the exact evaluation of the coupled-in microwave energy over a necessary measuring section length within the conveyor pipe, therefore relatively high microwave energies are necessary, which can also lead to reflections due to the undirected spreading-out or propagation, whereby these reflections interfere with the measuring signal and are only reducible through suitable time windows and thus only in a pulsed operation. For this purpose, however, a relatively high expense or effort is necessary for the coupling-in and coupling-out of the microwave energy and for the evaluation thereof.
A special antenna arrangement for the in-coupling of microwaves into a pipe-shaped hollow body, for the measurement of a volume proportion located therein, is known from the DE 94 12 243 U1, which makes possible a microwave radiation in one axial direction of the hollow body. This antenna arrangement is utilized for the filling level measurement in a pipe-shaped container, and includes a rod radiator antenna, which radiates out the microwave energy in one axial longitudinal direction of the pipe-shaped hollow body, of which the radiated energy in this direction comprises a high efficiency or degree of effectiveness. This rod radiator antenna would, however, be located in the conveyor stream in a pipe-shaped hollow body being flowed through, and here would not only interfere with the particle stream, but also be subjected to wear depending on the abrasion.
A further antenna arrangement for filling level measurement in a pipe-shaped hollow body is known from the DE 198 00 306 A1, which provides an axially directed microwave in-coupling by means of a so-called flat patch element. For that purpose, a planar radiator element is provided on the front end or end face of a hollow conductor or waveguide, whereby the planar radiator element essentially consists of a flat electrically conductive metal disk, which is applied on a plate-shaped dielectric substrate. An electrically conductive layer or a part of the metallic waveguide rear wall is applied above the dielectric substrate, and the high frequency energy is coupled-in therethrough. For that purpose, a coaxial connector is provided outside of the pipe wall, whereby the inner conductor is connected with the patch element and the outer conductor is connected with the metallic pipe wall or the electrically conductive layer. In that regard, the supplied microwave energy is coupled only in one axial direction into the pipe-shaped waveguide through the flat patch element, so that with this antenna arrangement nearly the entire microwave energy is radiated out in the measuring direction, whereby a high efficiency would be achievable with a targeted out-coupling over a measuring section or path. If one would, however, utilize such a patch element in a through-f lowable conveyor pipe, it would have to be arranged transversely in the conveyor stream and would similarly considerably impair the particle stream and would be subjected to wear by to the particle stream.